[A Case of MSI-H and Signet-Ring-Cell Carcinoma of the Colon].

The patient is a woman in her 70s. She came to our hospital because of constipation and abdominal pain. An abdominal CT scan showed a sigmoid colon mass and air in the surrounding mesentery, and an ileostomy was constructed based on the diagnosis of intramesenteric perforation of sigmoid colon cancer. Tumor biopsy by colonoscopy revealed a diagnosis of signet-ring-cell carcinoma. After 6 courses of mFOLFOX6 neoadjuvant chemotherapy, the patient underwent laparoscopic sigmoid colon resection and closure of the ileostomy. The final pathological diagnosis was pT4aN2aM0, pStage Ⅲc, RM1, microsatellite instability-high(MSI-H). Six courses of pembrolizumab chemotherapy were administered as adjuvant chemotherapy. Tumor markers have normalized and there are no signs of recurrence. MSI-H colorectal cancer is reported to account for about 10% of all colorectal cancers and signet-ring-cell carcinoma for only 1%. We report this case because it is a rare combination of both and a valuable case of successful multidisciplinary treatment.